Technical Field
This invention relates to systems and apparatuses for generating power from a flow of water.
Description of the Related Art
Many systems have been proposed for converting wave, tidal, current or fluvial flows into electricity. One type of device that is used in generating power is the free-stream underwater turbine usually driven by tidal flow. Deployed underwater, free-stream turbines can be deployed in an array but they require considerable separation between individual turbines to avoid mutual performance degradation.
In practice these devices also require a high flow velocity to enable the devices to be used for commercial energy production. Underwater free-stream turbines rely on the kinetic energy present in the water flow to generate power and are required to be positioned in the path of high velocity flows to be cost-effective without an unfeasibly large diameter. This is because the kinetic energy of the flow incident on the turbine disc is proportional to the square of the speed of the free-stream flow.
The theoretical largest fraction of the incident kinetic energy that can be turned into mechanical energy by any free-stream turbine is called the Betz limit. Beyond this point, the water simply flows around the outside of the turbine disc as if the turbine was a solid obstruction and contributes no further energy.
A further type of device used to generate power is a hydropower dam where a source of water channels all the water through the turbines located within the dam. However these types of systems require a head difference of 5 meters or more to enable the generators to work efficiently. This therefore limits the number of sites that such a system can be used.
The present invention provides an alternative apparatus for generating power from a flowing body of water, particularly in situations where there is a high volumetric flow of water at relatively low speed, slower than the speeds desirable for efficient energy product from a free-stream turbine. Furthermore the present invention is not subject to the Betz limit and is thereby suited to generating very large amounts of energy.